UPS systems are commonly used in installations such as data centers, medical centers and industrial facilities to provide backup power to maintain operation in event of failure of the primary utility supply. These UPS systems often have an “on-line” configuration including a rectifier and inverter coupled by a DC link that is also coupled to an auxiliary power source, such as a battery, fuel cell or other energy storage device. Other configurations, such as standby and line-interactive configurations, may also be used. UPS systems may have a modular structure including two or more UPS modules, each of which may include, for example, a rectifier, an inverter and a DC/DC converter for interfacing to a battery or other DC power source. The modules commonly are designed to operate in parallel to provide scalable power capacity, e.g., the modules may be coupled in common to an AC source, a DC source (e.g., a battery) and/or a load.
Power supply systems using UPSs, such as those used for data center applications, may be configured in a variety of different redundant configurations to increase reliability and availability. Various redundant UPS arrangements are described, for example, in U.S. Pat. No. 7,265,458 to Edelen et al.
As shown in FIG. 1, UPSs may be used in what is referred to an “A-B” configuration. A UPS 110 may have a first AC input 101 coupled to a power conversion chain including a rectifier 112 and an inverter 114 and a second AC input 102 coupled to a semiconductor static switch 116 that acts as a bypass. The UPS 110 may also include a DC/DC converter 118 coupled to a DC link between the rectifier 112 and the inverter 114 and configured to be coupled to a battery 10.
Both of the AC inputs 101, 102 of the UPS 110 may be coupled to a first source A. An AC output 103 of the UPS 110 may be coupled to a first static switch 122 of a separate dual switch assembly 120. A second static switch 124 of the dual switch assembly 120 may be coupled to a second AC source B, which may be another UPS. An output of the dual switch assembly 120 is coupled to a critical load 130. If the source A fails, the UPS 110 may provide power from its battery. If the UPS 110 fails, the load 130 may be served from the second source B via the second static switch 124 of the dual switch assembly 120.